A nuclear reactor in a nuclear plant has a reactor pressure vessel, RPV, which typically has a generally cylindrical shape and is closed in both ends, e.g., by a bottom head and a removable top head, to form a closed container. A core plate and a top guide are arranged inside the reactor pressure vessel with the top guide arranged on top of the core plate. The top guide comprises a number of holes. A reactor core in the form of fuel bundles is arranged inside the reactor pressure vessel with each fuel bundle being arranged through a hole in the top guide and resting on the core plate. Some reactors are provided with a core shroud which surrounds the core, the core plate and the top guide.
The reactor pressure vessel is filled with water covering the core and the shroud. The water in the reactor pressure vessel is arranged to flow through the core in order to cool the core during operation of the nuclear reactor. The flow is usually induced by circulation pumps arranged between the shroud and the nuclear reactor pressure vessel which makes the water flow downwards in the space between the shroud and the reactor pressure vessel wall. The circulation pumps may be of any of a number of different types.
In case of a so-called loss-of-coolant accident, LOCA, a rupturing of the recirculation duct system or the steam duct system during operation can cause coolant water to flow out of the reactor pressure vessel, thereby lowering the water level in the reactor pressure vessel and exposing the core in such a way that the fuel assemblies may be overheated and damaged. In order to prevent such overheating, the nuclear reactor comprises a core spray system including core spray supply piping, which is supplied via an inlet T-box assembly and connected to an upper tubular core spray sparger and a lower tubular core spray sparger above the core via a respective T-box assembly. The joints between the T-box assembly and the core spray spargers may be subjected to stress corrosion after long term use as acknowledged in U.S. Pat. No. 5,964,029. Such stress corrosion can result in cracks which can lead to leakage. Various methods and devices have been proposed for repairing such cracks.
U.S. Pat. No. 5,964,029 discloses a mechanical securing device adapted to secure and maintain a tubular cracked piping in a boiling water reactor. The known device comprises a first clamp operative to secure the device to a piping on one side of a crack, and a second clamp operative to secure the device to the piping on the opposite side of the crack. A bolt is connected between the clamps to exert an axial force tending to close the crack. A spring element disposed between the bolt and at least one of the clamps for maintaining a tensile force during thermal transients when the piping tends to contract due to the introduction of cold core spray water.
US 2006/0082139 discloses a core spray sparger T-box clamp apparatus adapted to be mounted to the T-box for a lower internal sparger inside a shroud of a reactor vessel.
U.S. Pat. No. 6,375,130 discloses an apparatus for clamping a core spray distribution header, comprising a first clamp on a first distribution header pipe, a second clamp on a second distribution header pipe and a connection body block connecting the first and second clamps. Each clamp has an upper clamp body and a lower clamp body. Also the connection body block has an upper body and a lower body.
For instance the T-box assemblies at the core spray spargers are provided at a location in the reactor pressure vessel, which is difficult to reach for maintenance, repair or replacement. Since the repair has to be performed under a short period of time, there is a need for an assembly which may be mounted in an easy and quick manner.